This project is designed to assess the ultrastructural localization of radiolabelled dopamine or its intermediary metabolites in the endocrine hypothalamus and the circumventricular organ system of the perinatal versus the reproductively competent rat brain. With the use of light and electron microscopic autoradiography coupled with double dimensional thin layer chromatography we will establish the neuroanatomical pattern (s) of dopamine (catechol) sensitive cellular (neuronal) compartments in the developing versus the adult brain. By establishing patterns of selective uptake (axonal vs. perikaryn recapture) we may be able to map these as potential receptor sites in the reputed role that biogenic amines have in the reg-ulation, of ovulatory and reproductive events. This may shed some light on the anatomic substrates and dynamic alterations that occur with the critical period of sexual differentiation. A pilot project is presently underway to assess the autoradiographic distribution of radiolabelled angiotensin II in selected circumventricular organs of the rat brain. The purpose here i to establish the precise ultrastructural localization of receptors for this powerful dipsogen in perinatal and adult rat brain and the ultrastructural correlates tha subserve thirst and waterbalance in the circumventricular organ system. The third and final component of this proposal will be a substantial expansion in our combined correlative SEM/TEM analysis of the perinatal and adult mammalian hypothalamus, medianeminence and other selected circumventricular organs. The purpose here is to delineate the fine structural correlates of the potential neuroendocrine role that circumventricular oergans, as well as periventricular and supraependymal neurons play in the potential control of the peripheral endocrine.